- Conference date: 17-31 June 2002
- Location: Pisa (Italy)
We considered 31,561 consecutive 64‐second values of radial solar wind speed reported by the SWEPAM instrument (D. McComas, Los Alamos, Principal Investigator) on the ACE spacecraft at L1 upstream of the earth’s bow shock beginning day 157 of the year 2000. Running values, moments and probability density functions (pdfs) were calculated for the speed differences over a range of lags from 64 seconds to several days. Running values show local intermittency in their amplitudes, and correlate with local solar wind speed. Moments of order greater than 6 are dominated by the largest values, which increase slowly with lag in the inertial range causing the exponent of the structure function at large q to be a straight line. The pdfs are compared to “Castaing distributions” which are superpositions of Gaussians whose standard deviations are log‐normally distributed. Although the Castaing distribution does not and in principle cannot precisely fit actual pdfs of velocity increments in the solar wind, it looks good and provides a basis for a handy two‐parameter description of the pdfs. The run of those two parameters with scale provides a further handy description of the intermittency in the cascade that is independent of any particular model of the cascade. Proving the disability of the Castaing distribution, the third moment of the longitudinal velocity increments does exist and it scales consistent with Kolmorogov’s 4/5 law that is a requirement for all theories of the inertial cascade.
- Probability density functions
- Solar wind
- Cumulative distribution functions
- Planetary bow shocks
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